Solubility and thermodynamics of glyphosate in aqueous solutions with various components and pH

In this study, the solubility of glyphosate in three binary mixed solutions (sodium chloride + water, triethylamine hydrochloride + water, and glyphosine + water) and aqueous solutions with different initial pH values was determined by a static method within the temperature range from 293.15 K to 353.15 K. Interestingly, the effects of different components on the solubility of glyphosate in aqueous solutions are quite different. The solubility of glyphosate at different initial pH shows a significant U-shaped characteristic, with the lowest solubility at about pH 1.5. In the binary mixed solutions, when the concentration of NaCl increases, the solubility of glyphosate first increases and then decreases. The increase of the triethylamine hydrochloride concentration has a negative effect on the solubility of glyphosate, while the increase of the glyphosine concentration has a positive effect on the solubility of glyphosate. The effect of pH on the solubility of glyphosate was correlated with a pH correlation model, and the solubility of glyphosate in the three mixed solutions was correlated with the modified Apelblat equation, λh equation, Jouyban-Acree-Apelblat (J-A-A) model and the non-randomness two-liquid (NRTL) model. The values of root mean square deviation (RMSD) indicate a good correlation of the model. In addition, the mixed thermodynamic properties (Δ_mixG, Δ_mixH, and Δ_mixS) of glyphosate in the three binary mixed solutions were calculated based on the NRTL model, and it was found that the mixing of glyphosate in all three systems was spontaneous, heat-absorbing and entropy-driven. The obtained solubility data and thermodynamic properties can provide theoretical guidance for the crystallization of glyphosate.